1. Field of Invention
The present invention relates to a power amplifier. More particularly, the present invention relates to a power amplifier for amplifying an audio signal.
2. Description of Related Art
As the name suggests, an audio amplifier amplifies audio signals. These audio amplifiers typically include an audio input stage and an audio output stage. The audio input stage is connected to some type of audio source and the audio output stage is connected to the audio device such as a speaker. These audio amplifiers receive audio signals from the audio source, amplify those audio signals, generate audio current signals based on those amplified signals, and output the audio current signals to the speaker. The audio current signals drive the speaker and cause the speaker to reproduce the audio signals that are generated by the audio source to create sound.
To amplify the audio signal, the amplifying circuit of the audio amplifier typically requires a bias circuit to provide bias voltages to bias the amplifying circuit. However, when the audio amplifier just powers on, the power source, such as the supply voltage, is suddenly applied to the bias circuit. This causes the bias voltage generated by the bias circuit to vibrate a lot. As a result, the output audio signal generated according to the bias voltage vibrates as well. This might damage the audio amplifier and produce unpleasant pop noises.
Therefore, there is a need for a new audio amplifier which can prevent the pop noise, and prevent the amplifier circuit from being damaged when the audio power amplifier powers on or powers down.